Field of the Invention
The invention relates to retrofit fixtures and systems and methods for lighting installations, and in particular, to fixtures, systems, and methods used to retrofit lighting installations with LED light sources.
Description of the Related Art
Troffer-style fixtures are ubiquitous in commercial office and industrial spaces throughout the world. In many instances these troffers house elongated tubular fluorescent lamps or light bulbs that span the length of the troffer. Troffers may be mounted to or suspended from ceilings, such as by suspension from a “T-grid”. Often the troffer may be recessed into the ceiling, with the back side of the troffer protruding into the plenum area above the ceiling. Typically, elements of the troffer on the back side dissipate heat generated by the light source into the plenum where air can be circulated to facilitate the cooling mechanism. U.S. Pat. No. 5,823,663 to Bell, et al. and U.S. Pat. No. 6,210,025 to Schmidt, et al. are examples of typical troffer-style fixtures.
More recently, with the advent of the efficient solid state lighting sources, these troffers have been used with LEDs as their light source. LEDs are solid state devices that convert electric energy to light and generally comprise one or more active regions of semiconductor material interposed between oppositely doped semiconductor layers. When a bias is applied across the doped layers, holes and electrons are injected into the active region where they recombine to generate light. Light is produced in the active region and emitted from surfaces of the LED.
LEDs have certain characteristics that make them desirable for many lighting applications that were previously the realm of incandescent or fluorescent lights. Incandescent lights are energy-inefficient sources with approximately ninety percent of the electricity they consume being released as heat rather than light. Fluorescent light bulbs are more energy-efficient than incandescent light bulbs by a factor of about 10, but are still relatively inefficient compared to LEDs, which can provide the same luminous flux as incandescent and fluorescent lights using a fraction of the energy.
In addition, LEDs can have a significantly longer operational lifetime. Incandescent light bulbs have relatively short lifetimes, with some having a lifetime in the range of about 750-1000 hours. Fluorescent bulbs can also have lifetimes longer than incandescent bulbs, such as in the range of approximately 10,000-20,000 hours, but provide less desirable color. In comparison, LEDs can have lifetimes between 50,000 and 70,000 hours. The increased efficiency and extended lifetime of solid state sources has resulted in widespread adoption of LEDs in place of conventional light sources in many different applications. It is predicted that further improvements will result in their general acceptance in more and more lighting applications. Movement toward universal usage of LEDs in place of incandescent or fluorescent lighting will result in increased lighting efficiency and significant energy saving.
There has been recent interest in upgrading existing troffer-style lighting systems with LED sources (or light engines) to capitalize on the above advantages. Current options for upgrading include complete fixture replacement such as by the commercially available CR Series Architectural LED Troffer, provided by Cree, Inc. Some features of these troffers are described in U.S. patent application Ser. No. 12/873,303, titled “TROFFER-STYLE FIXTURE”, and assigned to Cree, Inc. Performing complete fixture replacement can require penetrating the ceiling plenum by a skilled technician. This can be time consuming and expensive, and in many locations, building codes can require that a licensed electrician perform any work in the plenum space above a ceiling.
During the upgrade process, contamination may also be a concern, particularly in a hospital or clean room environment. In upgrade processes where the entire fixture is replaced, the sheet metal pan or housing of an existing troffer lighting system is removed. Removing the “host fixture” pan can generate dust which must be contained and cleaned prior to resuming normal operations within the environment. Preventing dust is of particular concern areas known to contain hazardous building materials, such as asbestos. In certain environments, construction permits may be required for an upgrade process that requires removal of the troffer pan, which can add additional complication and cost.
Another alternative upgrade option is by fixture retrofit where a new LED-based light engine can be installed into the sheet metal pan of an existing troffer lighting system. This can provide the advantage of using light engines with design features such as reflectors, lenses, and power supplies which have been optimized for an LED-based system. It also allows light engines which are approved for use in other applications to be used in a retrofit application. Examples of LED-based retrofit kits are discussed in detail in U.S. patent application Ser. No. 13/464,745, titled “MOUNTING SYSTEM FOR RETROFIT LIGHT INSTALLATION INTO EXISTING LIGHT FIXTURES”, which is commonly assigned with the present application to Cree, Inc. and incorporated by reference as if set forth fully herein. Some retrofits do not require the removal of the existing troffer pan prior to installation, with the pan acting as a barrier to the plenum space. Leaving the pan intact during the retrofit process does not disturb wiring connections, insulation, etc., above the ceiling plane. Leaving the pan in place can also allow for work to be performed by non-licensed personnel, which can eliminate costs for work that is required to be performed by licensed electricians. In some current retrofit products, replacement lamps or LED light engines are held into the existing fixture or sheet metal pan with brackets and screws. Some of these arrangements may require penetrating the ceiling, and some of these installations can be slow and labor-intensive.
Other upgrades involve replacing the fluorescent light bulbs/tubes with replacement tubes having LEDs along their length. This upgrade can utilize existing fluorescent lamp fixtures including the electrical ballast and wiring. However, compared to light engines designed to capitalize on the characteristics of LEDs, these replacement lamps can require much more energy for a given light output (lower efficacy), provide little to no cost benefit. In addition, the tubular format relies on the existing optical reflectors and lenses, which were designed for the light distribution characteristics of a fluorescent source.